I built and run a search engine and a "Wayback Machine" for Gemini:
gemini://kennedy.gemi.dev
There are ~4K hosts and ~1M documents/images/files which make for nice playground with experimenting with crawlers, indexers, and more. Its a nice hobby. Lots of primarily static sites, and CGI is used to add some interactivity:
gemini://gemi.dev/cgi-bin/moon.py